Stricture formation is a common complication of Crohn's disease resulting in severe morbidity, intestinal obstruction and surgical intervention. The overall objective of this proposal is to determine the pathologic mechanism of this stricturing process with the ultimate goal of providing modalities for therapeutic intervention. On the basis of our preliminary work, we proposed the hypothesis that these strictures result from increases in collagen and muscle in the bowel wall and that the accumulating collagen is synthesized by smooth muscle cells in response to chronic inflamation. Initial work on this project has demonstrated that collagen accumulation, smooth muscle cell proliferation and changes in the types of collagen normally present in the bowel wall, all play a role in the development of these strictures. In addition, the type of collagen that was increased in the strictures (type V) is produced predominately by smooth muscle cells. The results of these studies have therefore supported our hypothesis. An in vitro model of human intestinal smooth muscle (HISM) cells has been established and characterized. HISM cell collagen synthesis is selectively increased by serum and inhibited by protamine but not selectively inhibited by corticosteroids or heparin. In order to further test our hypothesis, the in vitro HISM cell model will be used to determine which defined inflammatory mediators stimulate or inhibit HISM cell collagen production and the types of collagen produced by HISM cells. The cellular mechanisms of control of HISM cell collagen production will be studied by: 1) examining protamines' and other mediators' inhibition of collagen production. Effects on HISM cell collagen mRNA levels, on mRNA transcription and on collagen degradation will be studied. 2) Determining whether second messengers such as cAMP and the Ca2+/phospholipid system are involved. The effects of cAMP, calcium, protein kinase C and diacylglycerol on HISM cell collagen production will be examined. Current technology available to the collagen biochemist and cell biologist has not been previously applied to the fibrosis complicating Crohn's disease. This proposal will provide information that will contribute significantly to an understanding of the mechanisms of stricture formation in this devastating disease and, hence, form the basis for future therapies to be used or its control and amelioration.